Single tooth restorations present the unique requirement that they must be supported non-rotationally on an underlying abutment. When a prepared natural tooth is the underlying abutment, this requirement is met in the normal course of preparing the abutment with a non-circular cross-section. Likewise, when the underlying abutment is a post fitted onto an implant, this requirement is met by preparing the post with a noncircular cross-section. This latter scenario can be more complicated due to the added connection between the implant and the abutment.
Typically, a dental implant is implanted into the bone of a patient's jaw and comprises a socket, e.g., a bore, which is accessible through the overlying or surrounding gum tissue for receiving and supporting one or more attachments or components which, in turn, are useful to fabricate and support the prosthodontic restoration. Dental implant procedures may use a variety of implanting modalities, for example, blade, threaded implant, or smooth push-in implant.
While numerous design iterations have been marketed, overall there have been three generations of the implant-abutment interface within these assemblies: an external hex implant, an internal connection implant, and a vertical connection assembly. The external hexagonal implant design has a hexagonal shape (or another anti-rotation feature) protruding out of the implant and the corresponding abutment has a female hexagonal receptacle. There is a surface below the hexagonal protrusion on which the abutment is seated. The hexagonal protrusion acts to constrain the abutment from rotating around the longitudinal axis as well as preventing movement on the plane coincident with the implant seating surface. Unfortunately, such an interface has virtually no stability until the screw is introduced and fully seated between the abutment and the implant. The screw is essentially the sole component resisting bending forces.
In contrast, the internal connection implant design has a hexagonal female member (or other anti-rotation feature) extruded into the implant, and the corresponding abutment has a male hexagonal protrusion. The abutment is seated on the same surface as the external hexagonal design, the only difference being that the anti-rotation feature on the implant is located below this surface. The benefit of this system is that it has intrinsic stability without the screw, and then experiences increased stability once the screw is introduced and fully seated. The system responds in a more unified manner to bending forces. While this system has advantages over the external hex implant, the disadvantage (which applies to the external hex as well) is that it is prone to leak at the implant-abutment interface (seating surface) due to “lifting” of the abutment under load that may create an intermittent gap resulting in bacteria penetration and subsequent crestal bone loss.
Another alternative interface is an internal/vertical connection implant assembly where the abutment sits “vertically” within the implant assembly and is supported by the internal sidewalls. In addition to this vertically interfacing aspect, many abutments contain a male anti-rotation feature at the bottom and the corresponding implants have a female receptacle (similar to the internal connection implant design). The main benefits of this design are that the two components effectively wedge together, creating a seal impenetrable to bacteria and the abutment receives added lateral support from the implant due to interaction of the abutment sidewalls with the interior surfaces of the implant. However, such designs suffer from vertical location variability. The accuracy of the fit of the final implant restoration (i.e., crown) is largely dependent on the ability to reliably transfer the location of the implant throughout the multiple steps involved in fabricating the restoration. The currently marketed vertical connection implant systems are susceptible to significant vertical location variability, and subsequent customer dissatisfaction. Location variability is undetectable until the very last step in the restorative process when the patient receives their restoration where it becomes apparent the restoration is too high or too low relative to the original tooth. For example, due to the required manufacturing tolerances, each time an abutment (or other male part) is mated with an implant (or other female part) the initial vertical position is destined to change. Further, once the parts are mated and torque is applied to the screw attaching the abutment to the implant, there is relative motion (or vertical displacement) between the male and female components. The magnitude of this motion is dependent on multiple variables, including but not limited to the screw torque, the surface finishes, and the component specifications.
Known vertical implant systems therefore still allow the lateral movement of the abutment in relation to the implant thus causing the possibility of misalignment. It would be desirable to have an abutment implant interface that eliminates vertical location variability. As the vertical connection implant assembly becomes accepted, it is necessary to develop a system that maintains the benefits of this type of design, yet eliminates the known vertical location variability problem. It would also be desirable for a system to create seals between the abutment and implant. The increase in seals in a contemplated system may result in adhesion between the implant and the abutment. Therefore it would be desirable for a removal system to assist in the removal of an abutment that adheres to an implant due to an improved interface.